1. Field of the Invention
This invention relates to a crop protection composition comprising a crop protection solid particle coated with a water-insoluble coating material. More specifically, this invention relates to a crop protection composition comprising an individual, mononucleate solid particle, which may be either a chemical crop protection solid particle, such as a herbicide, an acaricide, an insecticide, a miticide, a plant growth regulator, a fungicide or a nematicide, or a microbial crop protection solid particle, such as beneficial viruses, nematodes, fungi, bacteria or protozoa, coated with a water-insoluble coating material. The chemical or the microbial crop protection particle may be coated with either wood rosin, rosin derivatives, waxes, fatty derivatives, sterols, long-chain sterol esters or sulfur. Alternatively, the chemical or microbial crop protection particle may be coated with a water-insoluble latex polymer. In addition, the present invention relates to a mixture of such crop protection compositions with a partner which is also a solid particle.
2. Description of the Related Art
Encapsulation of an active component, such as a biocide, is disclosed in International Publication Number WO 95/08322. In this publication, "microcapsules" are prepared by dispersing or dissolving an active component or components in a solid matrix-forming material that has been thermally softened to form an encapsulation composition. The encapsulation composition is injected as an intact stream into a quenching liquid to provide solid microcapsules. What is termed "microcapsules" prepared by this method are really a plurality of particles randomly dispersed through a solidified droplet of coating material. These microcapsules do not have a single, mononucleate solid particle as a core surrounded by a wall of coating material. Moreover, the diameter of such microcapsules is not disclosed.
Large crop protection solid particles coated with water insoluble materials (i.e., particles having a diameter say, greater than 50 micrometers) clog screens and nozzles and thus, are not sprayable onto crops in the field. Known methods of coating or encapsulating small particles, (say, less than 50 micrometers) have serious process limitations. For instance, spray drying results in aggregates of tiny particles, or agglomerates, and requires solvent handling. Moreover, such agglomeration reduces the biological efficacy of the coated particles, since not all the particles are available for activity. Fluid bed coating is unsuited to small particles, such as powders, because tiny particles are difficult to fluidize in a fluid bed because interparticle forces are greater than those resulting from the action of the gas in the fluid bed. Particles are classified as Geldart Groups A, B, C and D. Geldart Group C powders, i.e., those less than 20 micrometers in diameter, are very difficult to fluidize. See Fluidization Engineering, Second Edition, Daizo Kunil and Octave Levenspiel, Butterworth-Heinmann Series in Chemical Engineering, ISBN 0-409-90233-0, pp 77-79. The Wurster process is not suited to coating small particles. Spinning disc processes are limited to particles larger than 50 micrometers, and require coating recovery/recycle steps. Such processes are also unsuited to non-spherical particle shapes and require a tight particle size range for uniform coating. With concentric nozzles, active ingredients are propelled through a coating composition. However, such a technique is unsuited to coating individual particles, and aggregates result. Moreover, coating recovery systems are required with concentric nozzles. Finally, chemical coacervation is a batch-type process that produces fine particle aggregates, is a dilute process, and requires extensive solvent recovery.
Coated particles made from the above-described techniques are also known. For instance, published European Patent Application 0 548 901 A1 discloses a microcapsule comprising agricultural active ingredients which is made by spray drying, which produces agglomerates as noted above. Moreover, this publication discloses the use of water soluble coatings, which can be hygroscopic and which are not useful for controlled release. European Patent Application 0 379 379 A2 discloses coated agrochemical and other particulate compositions, where the coating is formed by coacervation from at least two water soluble coacervating polymers. As noted above, coacervation requires extensive solvent recovery. Moreover, the '379 publication is directed toward coating liquid actives, which coated liquid actives have less tendency to settle in water than solids. Published International Application WO 94/22302 discloses coated biologically active particles and a process for making such particles by forming an aqueous suspension, emulsion or solution of a polymer or a polymer-forming precursor which is used for coating the suspended active particle. This coating process is not able to entirely coat a particle in one pass, as evidenced by the fact that a second coating layer is necessary in order to coat the areas which are not coated by the first coating layer. Published International Application WO 89/03638 discloses a pesticide composite composed of a substrate and a film of sulfonated polymer coating. The substrate is relatively large in size, i.e., 1-10 mm. (1,000 to 10,000 micrometers). At least one surface of the substrate is coated with a film of sulfonated polymer dissolved in a solvent system.
All of the publications discussed in the paragraph above require the material to be coated to first be suspended in a liquid to achieve coating, thus creating difficult solids recovery problems and generating large process waste streams. In addition, if such processes require water as the liquid, they cannot encapsulate water soluble particles.
Thus, there exists a need for coated crop protection solid particles having a very small diameter, say less than 50 micrometers, and which are non-agglomerated so that they may be sprayed without clogging a nozzle or screen. In addition, there exists a need for developing a process for coating or encapsulating particles with very small diameters, say less than 50 micrometers, which results in a high yield of small coated, yet non-agglomerated particles. In addition, there exists a need for a process which does not have attendant solids recovery problems or large process waste streams. Moreover, there exists a need for developing a process which can encapsulate water soluble solid particles, and for the resulting coated solid particles.